The present invention generally relates to electrophotographic printing devices and more specifically to the reduction of toner leakage through seals in these devices.
Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices such as laser printers and copiers use toner particles to form the desired image on the a print medium, which is usually some type of paper. While the toner particles are solid, their small size (on the order of 3-15 microns) results in highly fluid properties. Once the toner particles are is applied to the paper, the paper is advanced along the a paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner particles are is fused to the paper through a process of heat and pressure.
FIG. 1 is a diagram of typical laser printing device 100 employing an electrophotography (EP) process. For monochromatic printing, a single color of toner particles 101 are held in toner supply hopper 102. Toner particles 101 are typically small plastic (e.g. styrene) particles on the order of 5 microns (10-6) meter in size. Agitator, or stirring blade, 103 is typically made of plastic or mylar and ensures toner particles 101 are uniformly positioned along developer sleeve 104 while inducing a negative charge onto the toner particles 101 in the range of xe2x88x9230 to xe2x88x9240 micro coulomb per gram (xcexcC/g). Developer sleeve 104 rotates in a counterclockwise direction about an internal stationary magnet 105 which acts as a shaft. Toner particles 101 are attracted to the rotating developer sleeve 104 by the magnetic forces of stationary magnet 105. Doctor blade 106 helps in charging toner particles 101 and metes out a precise and uniform amount of toner particles 101 onto developer sleeve 104 as its outer surface rotates external to toner supply hopper 102. Developer sealing blade 107 removes excess toner particles 101 affixed to developer sleeve 104 as its outer surface rotates back into toner supply hopper 102.
Primary Charging Roller (PRC) 108 conditions Organic Photo Conductor (OPC) drum 109 using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum 109. Production of the uniform charge also has the effect of erasing residual charges left from the previous cycle.
A central component of the EP process is OPC drum 109. OPC drum 109 is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PRC 108. Initially, the unexposed surface of the OPC drum 109 is charged to a potential of approximately xe2x88x92600 volts. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a Charge Transport Layer (CTL), Charge Generation Layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC drum 109. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the aluminum substrate.
Laser beam 110 exposes OPC drum 109 one scan line at a time at the precise locations that will receive toner particles 101 (paper locations which correspond to the image being printed). OPC drum 109 is discharged from xe2x88x92600 V to approximately xe2x88x92100 V at points of exposure to laser beam 110, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles 101 are magnetically attracted to rotating developer sleeve 104. Alternatively, if nonmagnetic toner is used, developer sleeve 104 may comprise a foam roller to mechanically capture toner particles 101. In this case, an open cell foam roller may be included to apply toner particles 101 to developer sleeve 104. The still negatively charged toner particles 101 held by developer sleeve 104 is are attracted to the relatively positively charged (i.e., less negatively charged) areas of the surface of OPC drum 109 and xe2x80x9cjumpsxe2x80x9d across a small gap to the relatively positively charged latent image on OPC drum 109 creating a developed image.
Paper to receive the developed image from OPC drum 109 is transported along paper path 111 between OPC drum 109 and transfer roller 112, with the toner particles 101 forming the developed image are transferred from the surface of OPC drum 109 to the paper. The transfer occurs by action of transfer roller 112 which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles 101 to move to the paper. Wiper blade 113 cleans the surface of the OPC drum 109 by scraping off the waste (untransferred) toner particles 101 into waste hopper 115, while recovery blade 114 prevents the waste toner particles from falling back onto the paper. Fusing occurs as the paper, including transferred toner particles 101 is passed through a nip region between heated roller 116 and pressure roller 117 where the toner particles 101 is are melted and fused (or xe2x80x9cbondedxe2x80x9d) to the paper. Heated roller 116 and pressure roller 117 as a unit are referred to as the fuser assembly.
One design consideration with electrophotographic imaging devices such as laser printers and copying systems is the need to minimize the leakage of toner or toner particles 101 from toner supply hopper 102. As shown in FIG. 2, in its normal position, developer sleeve 104 has an enclosed toner supply on one side of the seal 201 and is open to the internal structure of the toner cartridge on the other side of the seal 201. Seals 201 in this area are incorporated in an attempt to reduce or eliminate toner leakage from toner supply hopper 102.
In addition to leakage along the a roller, leakage sometimes occurs at the ends of developer sleeve 104 (FIG. 1). Several methodologies have been used to reduce or eliminate such leakage. For example, i.e., some printers employ a foam or felt mechanical seal at the ends of developer sleeve 104 as a physical barrier to prevent toner particles 101 from leaking past the end of developer sleeve 104 and out of toner supply hopper 102. Alternatively, when the toner includes magnetic particles, such as in some black and white toners, magnetic seals may be provided at the ends of developer sleeve 104 to attract and capture toner particles 101 and create a physical barrier, consisting of the toner particles 101, to prevent additional toner particles 101 from leaking.
FIG. 2 shows another view of the configuration of developer sleeve 104, toner buildup 203 and seal 201. As shown, seal 201 is positioned between support 202 and developer sleeve 104. Support 203 may be semicircular regions formed in the sidewalls of toner supply hopper 102 allowing a rear portion of developer sleeve 104 to intrude into the toner supply hopper 102 to receive toner particles 101 while an exposed frontal portion of the developer sleeve 104 provides toner particles 101 to the OPC drum 109 as previously described. Because of the fluidity of the toner particles 101, as developer sleeve 104 rotates, toner particles 101 are forced into the region whereat seal 201 contacts developer sleeve 104. This action causes toner buildup 202 and corresponding increased toner fluid pressure in the contact region causing the toner particles 101 to leak under, around and through seal 201.
Accordingly, a need exists for a system and a method for reducing toner leakage in a toner cartridge.
The present invention is directed to a sealing mechanism for use in a toner cartridge comprising a developer roller having an undulant annular channel and a flexible seal having a follower configured to engage the undulant annular channel. The flexible seal is configured such that rotation of the developer roller induces a laterally reciprocating motion of the flexible seal with respect to the developer roller. Another embodiment of the present invention is directed to a method of reducing toner leakage in a toner cartridge by engaging a follower with a the first flexible seal within an undulant annular channel formed in the developer roller, rotating the developer roller thereby inducing a laterally reciprocating motion in a first flexible seal and applying toner to the developer roller in a vicinity of the first flexible seal whereby the laterally reciprocating motion of the first flexible seal sweeps the toner in a direction away from the undulant annular channel.